# Structural Biochemistry/Pharmacodynamics

## Pharmacodynamics

Pharmacodynamics is a subdivision of pharmacology that deals with the physiological effects of chemicals on the biological systems from viruses to bacteria to even multicellular systems within the body. This area also looks into the mechanisms of chemical action and the relationship between drug concentration and effect. An example of drug with receptor interactions can be modeled by

${\displaystyle D+R\ \rightleftharpoons \ D\!\cdot \!R}$

such that D is the chemical or drug, R is the receptor or binding site, and D·R is the chemical bound to the receptor. These reaction dynamics can mathematically be studied using tools like free energy maps.

## Pharmacokinetics

Pharmacokinetics is the other subdivision of pharmacology that focuses on the absorption, distribution, and excretion of drugs while passing through the body with focus on dimension of time. It is difficult for researchers to track where the medicines are traveling, thus they use mathematical methods to measure body fluids to determine where the drug travels and the percentage of remaining drug product left in the body. The amount of drug absorbed can be predicted from measuring the blood levels of liver enzymes. The chemistry aspect of pharmacokinetics studies the chemical interactions between drug and body molecules in biological environment. This can help researchers to determine how much of a drug the body can take in and thus alters the packaging of medicines to the patients. Pharmacodynamics is abbreviated as "PD" while pharmacokinetics is abbreviated as "PK".[1] The pharmacokinetics of any type of medication truly relies on several different factors involving the patients background. These factors include genetic history of the patient, sex, and age. Other factors that influence the delivery of medication also lie within the chemical structure of the drug. Age factors can affect the speed at which a drug is metabolized. For example, Fig. 1 compares the rates of metabolism of diazepam between a younger man and an elderly one. The graph shows that the elderly man metabolizes less of the drug over a longer a period of time than the younger man.

Other types of factors can affect pharmacokinetics. In general the overall health of an individual plays a major role in drug metabolism and absorption. Health issues such as renal failure or kidney problems can greatly reduce the rate at which a drug is absorbed by the body. Regardless, these factors are all compensated by physicians through the use of formulas that describe the specific parameters surrounding the stages of pharmacokinetics. With these equations, physicians and pharmacists can correctly and accurately provide the necessary dosage of medications to help the patient.

## References

Davis, Alison Davis. Medicines By Design. The Office of Communications and Public Liaison. 2006.

1. Davis, Alison Davis. Medicines By Design. The Office of Communications and Public Liaison. 2006.